This invention relates to a method and apparatus for blanking and inserting foil membranes into reusable covercaps. More particularly, the invention relates to a method and apparatus for automatically inserting coated aluminum foil membranes into plastic covercaps in one continuous punch stroke by blanking a foil membrane with a pull tab, folding the tab and inserting the membrane into the cap.
Resealable packages, such as food packages, may include a removable sealing membrane and a reusable covercap for reclosing the container after opening. Such containers, which may be metal or composite containers, usually have the removable sealing membrane secured to the mouth of the container by induction heat sealing. Such membranes may include a disc portion and an integral tab portion which may be reverse folded about a line adjacent the periphery of the membrane disc portion and sandwiched between the membrane disc and the covercap. The tab portion facilitates removal of the membrane from the container after removal of the covercap.
It is known in the art to blank disc-shaped metal foil having integral tab portions. U.S. Pat. No. 2,901,994, issued Sept. 1, 1959, discloses an apparatus for making metal foil closure hoods with an integral tear tab. The patent discloses a tab cutting and folding mechanism for precutting the tab and folding it over the top of the foil membrane into the circular area from which the hood is to be made. The tab cutting mechanism, which is provided one feed step ahead of the hood blanking step, includes a hollow punch with a beveled surface and folding fingers. U.S. Pat. No. 2,148,906, issued Feb. 28, 1939, discloses an apparatus for the manufacture of container caps having a finger tab with a pattern for gripping. When the cap blank has been punched out, a punch and female drawing sleeve continue downwardly such that the tab is held sandwiched between two stamping portions of the mechanism during the drawing operation of the container cap.
It is also known in the art to combine blanking of the membrane with insertion of the membrane into a cap. U.S. Pat. No. 2,100,596, issued Nov. 30, 1937, and U.S. Pat. No. 3,959,061, issued May 25, 1976, disclose methods and apparatus for inserting generally disc shaped membranes into container caps wherein the blanking and inserting steps are accomplished in one continuous press stroke.
For membranes having a disc portion and integral tab portion, a precise fold of the tab is necessary in order to achieve a proper induction heat seal. For example, a fold too close to the center of the disc portion of the membrane will cause a "leaker" which can be defined as a membrane that has not been properly sealed entirely around the periphery of the container mouth and which will result in leakage of the container contents from the improperly sealed package. Furthermore, a fold too far from the center of the disc may result in excessive metal at the edge of the disc at the point of induction heat sealing. The excessive metal acts as a heat sink which precludes reaching of the proper bonding temperature and results in either unsealed membranes or membranes that can be accidentally unsealed. U.S. Pat. No. 3,892,351, issued July 1, 1975, discloses an attempt to facilitate uniform heat distribution during the heat sealing step by the use of holes or elongated openings in the region where the tab joins the circular disc portion of the foil membrane. Another patent, U.S. Pat. No. 3,961,566, issued June 8, 1976, shows the use of fold lines to define the tab portion of the membrane in order to facilitate bending of the tab.
Attempts have also been made, as shown in U.S. Pat. Nos. 3,501,045, issued Mar. 17, 1970, and 3,734,044, issued May 22, 1973, to provide easy opening of such containers and to reduce the amount of scrap foil material resulting from blanking membranes from foil stock. It is also known, for example, in U.S. Pat. No. 3,328,873, issued July 4, 1967, and U.S. Pat. No. 4,047,473, issued Sept. 13, 1977, to use a vacuum head to hold a blanked membrane in position before insertion into the covercap.
Such prior art methods and apparatus are not without shortcomings however. There still exists a need to automate blanking and inserting of aluminum foil membranes into plastic covercaps particularly suited for induction heat sealed containers. It is desirous that the blanking and inserting be done simultaneously in one operation, preferably, in one stroke of a blanking punch. Furthermore, the blanking and inserting of multiple membranes in one operation would be further suited for high speed production lines. In order to accomplish such blanking and inserting in one operation, a machine should be able to blank the membrane disc and integral tab portions, to fold the tab accurately without tears to provide good quality membranes for induction heat sealing to containers, and to insert the blanked membrane into covercaps.